With oil temperatures below ˜80° C., for example, it is advantageous if the oil flow bypasses the radiator so that the transmission reaches the operating temperature faster. In this way, the efficiency of the transmission is increased. In addition, it is necessary to provide devices to protect the radiator against pressure peaks, which is normally carried out by way of a separate bypass valve.
From U.S. Pat. No. 5,890,509, a bypass valve is known that is arranged in a hydraulic circuit between a torque converter and the lubrication circuit. This valve comprises a valve coil, which acts against the force of a compression spring so that, in the bypass-mode, fluid from the torque converter flows directly into the lubrication circuit without being conveyed through the radiator and/or heat exchanger. In addition, a viscosity-sensitive pressure distributor is provided. This produces pressure in the direction of the force of the compression spring when the temperature rises so that the valve coil is displaced into a cool position, which results in the fluid in the torque converter is conveyed through the heat exchanger.
Furthermore, from US 2004/0204281, A1 a cooling system for the operating fluid of an automatic transmission is known, which comprises a water-cooled oil radiator and an air-cooled oil radiator, which are connected in series, as well as a first bypass valve, such that operating fluid bypasses both coolers when the temperature is T≦T1, where T1 is a predefined threshold value. In addition, a second bypass valve is provided which, in the disengaged state allows the fluid to flow through the water-cooled radiator when the temperature is T≦T2, where T2 is a predefined threshold value.
Moreover, a bypass device for a heat exchanger is known from U.S. Pat. No. 6,253,837 B1, which comprises a bypass valve, such that the oil flow bypasses the radiator when there is a predefined temperature interval. The bypass valve comprises a housing with three openings, wherein one of the openings serves as a valve opening. In addition, a temperature-sensitive actuator is provided in the housing, which is operationally connected to a spring valve, so that the valve opening is opened or closed subject to the temperature. To accomplish this, the valve opening can be connected to the inlet or outlet of the heat exchanger.
The present invention is based on the task of specifying a device for uncoupling the oil flow through a radiator, in particular a radiator for a transmission, that can be manufactured and assembled inexpensively. In addition, the pressure peaks in the supply to the radiator ought to be largely eliminated without requiring a separate bypass valve.